1. Field of the Invention
The present invention relates to rotary piston engines and more particularly to intake systems for rotary piston engines. More specifically, the present invention pertains to intake systems for rotary piston engines wherein the pressure pulsations produced in one working chamber are transmitted to the intake port for another working chamber to thereby produce a supercharging effect.
2. Description of the Prior Art
In rotary piston engines, it has already been proposed to utilize the pressure pulsations produced at the intake port for obtaining a supercharging effect. For example, the U.S. Pat. No. 3,491,733 discloses a single rotor type rotary piston engine which has an intake system including two intake passages of different lengths so that pressure resonance effect can be obtained at different engine speeds. The concept of obtaining a supercharging effect in the patent is to produce a pressure resonance in the intake passage leading to a single working chamber. When the concept is applied to a multiple rotor type rotary piston engine, the pressure resonance is produced in each one of the individual intake passages leading from the intake manifold to the respective ones of the working chambers. Therefore, the individual intake passages must be of substantial lengths in order that the pressure resonance effect is obtained in a normal operating speed of the engine. Further, there must be provided at least two individual intake passages for each rotor chamber so that the pressure resonance effect is utilized in a wide range of engine speed.
It has been recognized in rotary piston engines having intake ports formed in side housings that there is an overlap between the intake port and the exhaust port in the very beginning of the intake stroke so that there is a noticeable quantity of residual combustion gas in the working chamber and the residual combustion gas produces a compression wave in the intake passage in the vicinity of the intake port in the instance when the intake port is opened. The U.S. Pat. No. 4,562,804 proposes to utilize the pressure wave thus produced in the intake port for one working chamber to supercharge another working chamber. According to the proposal, the opening timing of the intake port and the length of the passage from the intake port for one working chamber to the intake port for another working chamber is properly determined so that the pressure wave produced at the intake port for the one working chamber is transmitted to the intake port for the other working chamber at the final period of the intake stroke of the other working chamber under an engine speed range wherein a high output power is required. The proposal by the U.S. patent is specifically for two rotor type rotary piston engines and the proposed structure is limited to an application for the two rotor type engines.
It has now been found by the inventors that in rotary piston engines having three or more rotors that the pressure waves produced in the intake ports for the respective working chambers influence with each other so that it is not easy to utilize the pressure waves for supercharging. It has also been found by the inventors that under a specific condition it is possible to obtain a useful interaction between the pressure waves so that an effective supercharging can be obtained by utilizing the pressure waves.